Pure boron for silicide contact

ABSTRACT

A semiconductor device includes a gate disposed over a substrate; a source region and a drain region on opposing sides of the gate; and a pair of trench contacts over and abutting an interfacial layer portion of at least one of the source region and the drain region; wherein the interfacial layer includes boron in an amount in a range from about 5×10 21  to about 5×10 22  atoms/cm 2 .

DOMESTIC PRIORITY

This application is a continuation of and claims priority from U.S.patent application Ser. No. 15/248,002, filed on Aug. 26, 2016, entitled“PURE BORON FOR SILICIDE CONTACT,” which is a continuation of and claimspriority from U.S. Pat. No. 9,484,431, issued on Nov. 1, 2016, entitled“PURE BORON FOR SILICIDE CONTACT,” each application is incorporatedherein by reference in its entirety.

The present invention generally relates to metal-oxide-semiconductorfield-effect transistors (MOSFET), and more specifically, tosource/drain contact structures.

The MOSFET is a transistor used for amplifying or switching electronicsignals. The MOSFET has a source, a drain, and a metal oxide gateelectrode. The metal gate is electrically insulated from the mainsemiconductor n-channel or p-channel by a thin layer of insulatingmaterial, for example, silicon dioxide or glass, which makes the inputresistance of the MOSFET relatively high. The gate voltage controlswhether the path from drain to source is an open circuit (“off”) or aresistive path (“on”).

N-type field effect transistors (NFET) and p-type field effecttransistors (PFET) are complementary MOSFETs. The NFET uses electrons asthe majority current carriers and is built directly on a p-typesubstrate with n-doped source and drain junctions (also called epitaxialcontacts) and an n-doped gate. The PFET uses holes as the majoritycurrent carriers and is built on an n-well with p-doped source and drainjunctions (epitaxial contacts) and a p-doped gate. The dopantconcentration in the source and drain junctions is an importantparameter for optimal transistor function.

SUMMARY

In one embodiment of the present invention, a semiconductor deviceincludes a gate disposed over a substrate; a source region and a drainregion on opposing sides of the gate; and a pair of trench contacts overand abutting an interfacial layer portion of at least one of the sourceregion and the drain region; wherein the interfacial layer includesboron in an amount in a range from about 5×10²¹ to about 5×10²²atoms/cm².

In another embodiment, a method of making a semiconductor deviceincludes performing an epitaxial growth process to form epitaxialcontacts on opposing sides of a gate positioned over a substrate;removing portions of the epitaxial contacts to form trench contactpatterns; depositing a conformal layer including amorphous boron withinthe trench contact patterns, the conformal layer forming a discreteinterfacial layer within the epitaxial contacts, and the discreteinterfacial layer including boron in an amount in a range from about5×10²¹ to about 5×10²² atoms/cm²; removing the conformal layer includingamorphous boron; and filling the trench contact patterns with a high-kdielectric material and a conductive metal to form the trench contacts.

Yet, in another embodiment, a method of making a semiconductor deviceincludes performing an epitaxial growth process to form epitaxialcontacts on opposing sides of a gate positioned over a substrate;removing portions of the epitaxial contacts to form trench contactpatterns; performing a deposition process to deposit a conformal layerincluding substantially pure amorphous boron within the trench contactpatterns, the conformal layer forming a discrete interfacial layerwithin the epitaxial contacts comprising boron in an amount in a rangefrom about 5×10²¹ to about 5×10²² atoms/cm²; removing the conformallayer including amorphous boron; and filling the trench contact patternswith a high-k dielectric material and a conductive metal to form thetrench contacts.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIGS. 1-7 illustrate an exemplary method of making a PFET source/draincontact according to embodiments the present invention, in which:

FIG. 1 is a cross-sectional side view of a semiconductor device with aPFET and a NFET formed over a substrate;

FIG. 2 is a cross-sectional side view after performing an etchingprocess to form trench contacts over the source/drain regions;

FIG. 3 is a cross-sectional side view after lithographic patterning toblock the NFET region;

FIG. 4A is a cross-sectional side view after depositing a conformallayer of amorphous boron;

FIG. 4B is a cross-sectional side view after removing the amorphousboron layer;

FIG. 4C is a cross-sectional side view after removing the lithographicpatterning mask;

FIG. 5A is a cross-sectional side view after depositing a liner in thetrench contacts;

FIG. 5B is a cross-sectional side view after filling the trench contactwith a conductive metal;

FIG. 6A is a cross-sectional side view after depositing an oxide layerover the semiconductor device;

FIG. 6B is a cross-sectional side view after etching to form the gatecontact patterns over the gates; and

FIG. 7 is a cross-sectional side view after depositing a gate contactliner and conductive gate material.

DETAILED DESCRIPTION

Although the dopant concentration (e.g., boron (B) concentration) cansignificantly improve functioning at the PFET source/drain contact, theability to increase the dopant concentration by ion implantation orother methods (e.g., in-situ based doping) is limited to an upper limitof about 5×10²⁰ atoms/centimeter² (atoms/cm²).

Accordingly, embodiments of the present invention provide a PFETsource/drain contact with a high boron concentration in silicon (Si) orsilicon germanium (SiGe), up to about 3×10²² atoms/cm². Further, theboron mixes with the Si or SiGe with to provide high activity in thecontact because a high boron concentration provides decreasedresistance. A method of making the PFET source/drain contact with a highboron concentration (e.g., 1×10¹⁹ to about 1×10²¹ atoms/cm²) is nowdescribed in detail with accompanying figures. It is noted that likereference numerals refer to like elements across different embodiments.

The following definitions and abbreviations are to be used for theinterpretation of the claims and the specification. As used herein, theterms “comprises,” “comprising,” “includes,” “including,” “has,”“having,” “contains” or “containing,” or any other variation thereof,are intended to cover a non-exclusive inclusion. For example, acomposition, a mixture, process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but can include other elements not expressly listed or inherentto such composition, mixture, process, method, article, or apparatus.

As used herein, the articles “a” and “an” preceding an element orcomponent are intended to be nonrestrictive regarding the number ofinstances (i.e. occurrences) of the element or component. Therefore, “a”or “an” should be read to include one or at least one, and the singularword form of the element or component also includes the plural unlessthe number is obviously meant to be singular.

As used herein, the terms “invention” or “present invention” arenon-limiting terms and not intended to refer to any single aspect of theparticular invention but encompass all possible aspects as described inthe specification and the claims.

As used herein, the term “about” modifying the quantity of aningredient, component, or reactant of the invention employed refers tovariation in the numerical quantity that can occur, for example, throughtypical measuring and liquid handling procedures used for makingconcentrates or solutions. Furthermore, variation can occur frominadvertent error in measuring procedures, differences in themanufacture, source, or purity of the ingredients employed to make thecompositions or carry out the methods, and the like. In one aspect, theterm “about” means within 10% of the reported numerical value. Inanother aspect, the term “about” means within 5% of the reportednumerical value. Yet, in another aspect, the term “about” means within10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

Turning now to the Figures, FIGS. 1-7 illustrate an exemplary method ofmaking a PFET source/drain contact according to embodiments of presentinvention. FIG. 1 is a cross-sectional side view of a semiconductordevice with a NFET 150 and a PFET 151 formed over a common substrate101. Non-limiting examples of suitable substrate materials includesilicon, silicon dioxide, aluminum oxide, sapphire, germanium, galliumarsenide (GaAs), an alloy of silicon and germanium, indium phosphide(InP), or any combination thereof. Other examples of suitable substrates101 include silicon-on-insulator (SOI) substrates with buried oxide(BOX) layers. The thickness of the substrate 101 is not intended to belimited. In one aspect, the thickness of the substrate 101 is in a rangefrom about 2 mm to about 6 mm for bulk semiconductor substrates. Inanother aspect, the thickness of the substrate 101 is in a range fromabout 25 nm to about 50 nm for the silicon layer in SOI substrates

To form the epitaxial contacts forming the source regions 120 and 122and the drain region 121 and 123, lithography and etching are performed.Lithography can include depositing a photoresist (not shown) onto thesubstrate 101 and developing the exposed photoresist with a resistdeveloper to provide a patterned photoresist. The epitaxial contacts areformed by performing an epitaxial growth process to deposit a dopedmaterial (e.g., silicon). The type of dopant used depends on whether theMOSFET is the NFET 150 or the PFET 151. Non-limiting examples ofsuitable dopants for the NFET 150 include n-type dopants (e.g., Group Velements such as phosphorus). Non-limiting examples of suitable dopantsfor the PFET 151 include p-type dopants (e.g., Group III such as boron).Generally, the concentration of dopant in the epitaxial contacts is in arange from about 1×10¹⁹ to about 1×10²¹ atoms/cm².

The thickness of the epitaxial contacts forming the source regions 120and 122 and the drain regions 121 and 123 is not intended to be limited.In one aspect, the thickness of the epitaxial contacts is in a rangefrom about 5 nm to about 60 nm. In another aspect, the thickness of theepitaxial contacts is in a range from about 5 nm to about 10 nm.

The gates 110 and 112 are formed by lithographic patterning and etching.Initially, a “dummy gate” is formed by filling the gate region with asuitable removable gate material, for example, amorphous silicon(polysilicon). The removable gate material is subsequently removed, andthe gates 110 and 112 are filled with a conductive gate material. Ahigh-k dielectric liner can be deposited before filling with theconductive gate material.

The high-k dielectric material can be a dielectric material having adielectric constant greater than 4.0, 7.0, or 10.0. Non-limitingexamples of suitable materials for the high-k dielectric materialinclude oxides, nitrides, oxynitrides, silicates (e.g., metalsilicates), aluminates, titanates, nitrides, or any combination thereof.Other non-limiting examples of suitable high-k dielectric materialsinclude HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, Y₂O₃, apervoskite oxide, or any combination thereof. The high-k dielectricmaterial layer may be formed by known deposition processes, for example,chemical vapor deposition (CVD), plasma-enhanced chemical vapordeposition (PECVD), atomic layer deposition (ALD), evaporation, physicalvapor deposition (PVD), chemical solution deposition, or other likeprocesses. The thickness of the high-k dielectric material may varydepending on the deposition process as well as the composition andnumber of high-k dielectric materials used. The high-k dielectricmaterial layer may have a thickness in a range from about 0.5 to about20 nm.

Non-limiting examples of suitable conductive gate metals includealuminum (Al), platinum (Pt), silver (Au), tungsten (W), titanium (Ti),or any combination thereof. The conductive metal may be deposited by aknown deposition process, for example, CVD, PECVD, PVD, plating, thermalor e-beam evaporation, and sputtering.

The thickness of the gates 110 and 112 is not intended to be limited. Inone aspect, the thickness of the gates 110 and 112 is in a range fromabout 20 nm to about 75 nm. In another aspect, the thickness of thegates 110 and 112 is in a range from about 20 nm to about 50 nm.

A blanket oxide layer 130 is deposited onto both NFET 150 and PFET 151regions over the substrate 101. Non-limiting examples of suitablematerials for the oxide layer 130 include flowable oxides (e.g., liquidsolutions of hydrogen silsesquioxane in a carrier solvent) and silicondioxide. The thickness of the oxide layer 130 is not intended to belimited. In one aspect, the thickness of the oxide layer 130 is in arange from about 50 nm to about 150 nm. In another aspect, the thicknessof the oxide layer 130 is in a range from about 60 nm to about 115 nm.

An optional silicon nitride (SiN) layer 140 is deposited onto the oxidelayer 130. The thickness of the SiN layer 140 is not intended to belimited. In one aspect, the thickness of the SiN layer 140 is in a rangefrom about 5 nm to about 20 nm. In another aspect, the thickness of theSiN layer 140 is in a range from about 10 nm to about 15 nm.

FIG. 2 is a cross-sectional side view after performing an etchingprocess to form trench contacts 201 over the source regions 120 and 122and drain regions 121 and 123. The etching process may be a dry etchingprocess, for example, reactive ion etching (RIE). The etching process isperformed through the SiN layer 140, the oxide layer 130, and a portionof the epitaxial contacts of the source regions 120 and 122 and drainregions 121 and 123. The etching process removes a portion of and stopswithin a region of the epitaxial contacts to form a recess. The opentrench contacts 201 form a trench contact pattern. The trench contactpatterns have side walls (y) and a base (x) that protrude into theepitaxial contacts of the source region 122 and the drain region 123.

FIG. 3 is a cross-sectional side view after lithographic patterning toblock the NFET 150 region. A hard mask layer 301 is deposited over theNFET 150 portion of the substrate 110. The hard mask layer 301 mayinclude, for example, amorphous carbon (a-C), silicon nitride (SiN), orsilicon dioxide (SiO₂). The hard mask layer 301 fills the open regionsof the trench contacts 201.

FIG. 4A is a cross-sectional side view after depositing a conformallayer of amorphous boron. The amorphous boron layer 401 is formed byusing a deposition process (e.g., CVP or ALD) to deposit a conformallayer of amorphous boron within the trench contacts 201 over the PFET151. The amorphous boron layer 401 includes substantially pure boron. Inone embodiment, the amorphous boron layer 401 includes 100 atomic % (at.%) boron. In another embodiment, the amorphous boron layer 401 includesat least 99 at. % boron. Yet, in another embodiment, the amorphous boronlayer 401 includes at least 98 at. % boron.

Deposition of the amorphous boron layer 401 may be performed by ChemicalVapor Deposition (CVD). The conditions of the CVD process may betailored to the particular semiconductor device. The CVD process may beperformed at atmospheric pressure (i.e., about 760 Torr), or reducedpressures, for example 60 Torr or 36 Torr. In one exemplary embodiment,the deposition is performed at processing temperatures ranging fromabout 500° C. to about 800° C. Diborane (B₂H₆) is injected into thereactor chamber as the dopant gas at a flow rate of, for example, 490standard cubic centimeters per minute (sccm). Hydrogen gas (H₂) may beused as the carrier gas and for dilution of the doping source.

The hard mask layer 301 protects the trench contacts 201 over the NFET150 region. The amorphous boron layer 401 lines the trench contacts 201of the PFET 151 and forms an interfacial layer 410 including a highboron concentration in the epitaxial contacts of the source region 122and drain region 123. The interfacial layer 410 naturally forms in thesource region 122 and drain region 123 upon disposing amorphous boronlayer 401 within the trench contacts 201.

In one aspect, the interfacial layer 410 has a thickness in a range fromabout 0.5 nm to about 2 nm. In another aspect, the interfacial layer 410has a thickness in a range from about 1 nm to about 1.5 nm. Yet, inanother aspect, the interfacial layer 410 has a thickness about or inany range from about 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1., 1.2, 1.3, 1.4,and 1.5 nm.

In one aspect, the interfacial layer 410 has a boron concentration in arange from about 5×10²¹ to about 5×10²² atoms/cm². In another aspect,the interfacial layer 410 has a boron concentration in a range fromabout 1×10²² to about 3×10²² atoms/cm².

FIG. 4B is a cross-sectional side view after removing the amorphousboron layer 401. The amorphous boron layer 401 may be removed using anysuitable process. Although the amorphous boron layer 401 is stripped,the interfacial layer 410 remains over the source region 122 and thedrain region 123. In one non-limiting example, a boiling solution ofconcentrated nitric acid (HNO₃) is used to remove the amorphous boronlayer 401. The temperature of the HNO₃ can be, for example, 110° Celsius(° C.). The concentration of the HNO₃ can be, for example, between about50 and about 85%. In another non-limiting example, an aqua regia processcan be used to remove the amorphous boron layer 401. An aqua regiaprocess involves using a nitro-hydrochloric acid (HCl) to etch away theamorphous boron layer 401. The nitro-HCl mixture is formed by mixingconcentrated nitric acid and hydrochloric acid in a volume ratio of, forexample, 1:3.

FIG. 4C is a cross-sectional side view after removing the hard masklayer 301 over the NFET 150 region. The hard mask layer 301 can beremoved by a wet cleaning process using, for example, HF or HCl and dryetching. Suitable dry etching processes include RIE, plasma etching, ionbeam etching, laser ablation, or any combination thereof.

FIG. 5A is a cross-sectional side view after depositing a liner 501 inthe trench contacts 201. To form the liner 501, a high-k dielectricmaterial is deposited into the trench contacts. The high-k dielectricmaterial can be a dielectric material having a dielectric constantgreater than 4.0, 7.0, or 10.0. Non-limiting examples of suitablematerials for the high-k dielectric material include oxides, nitrides,oxynitrides, silicates (e.g., metal silicates), aluminates, titanates,nitrides, or any combination thereof. Other non-limiting examples ofsuitable high-k dielectric materials include HfO₂, ZrO₂, Al₂O₃, TiO₂,La₂O₃, SrTiO₃, LaAlO₃, Y₂O₃, a pervoskite oxide, or any combinationthereof. The high-k dielectric material layer may be formed by knowndeposition processes, for example, CVD, PECVD, ALD, evaporation, PVD,chemical solution deposition, or other like processes. The thickness ofthe high-k dielectric material may vary depending on the depositionprocess as well as the composition and number of high-k dielectricmaterials used.

In one embodiment, the liner 501 includes a bilayer of Ti and TiN. TheTiN is deposited over the layer of Ti to form the Ti/TiN liner. Thethickness of the liner 501 can generally vary and is not intended to belimited. In one aspect, the thickness of the liner 501 is in a rangefrom about 3 nm to about 10 nm. In another aspect, the thickness of theliner 501 is in a range from about 4 nm to about 9 nm.

FIG. 5B is a cross-sectional side view after filling the trench contacts201 with a conductive metal 501. Non-limiting examples of suitableconductive metals include tungsten, aluminum, platinum, gold, or anycombination thereof. A planarization process, for example chemicalmechanical planarization (CMP), is performed over the conductive metal501. The conductive metal may be deposited by a known depositionprocess, for example, CVD, PECVD, PVD, plating, thermal or e-beamevaporation, and sputtering.

FIG. 6A is a cross-sectional side view after depositing a blanket oxidelayer 601 over the NFET 150 and PFET 151 regions of the semiconductordevice. The oxide layer 601 can include, for example,tetraethyl-ortho-silicate (TEOS) or silicon dioxide.

FIG. 6B is a cross-sectional side view after etching to form the gatecontact patterns 610 over the gates 110 and 112. In one non-limitingexample, a RIE process is performed to form the gate contact patterns610.

FIG. 7 is a cross-sectional side view after depositing a gate contactliner 701 and conductive gate material 702 into the gate contactpatterns 610. The gate contact liner 701 can include, for example, ahigh-k dielectric material as described above for liner 501 (see FIG.5A). The conductive gate material 702 can be any of the conductive metalmaterials described above for the trench contacts 201 (see FIG. 5B). Aplanarization process, for example, a CMP process, is performed over theconductive gate material 702.

The above described embodiments of semiconductor devices and methods ofmaking such devices provide various advantages. The methods provide aPFET source/drain contact with a high boron concentration in Si or SiGe,up to about 3−5×10²² atoms/cm². After depositing a layer of amorphousboron over the source and drain a contact, the boron mixes with the Sior SiGe with to provide high activity in the contact.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The flow diagrams depicted herein are just one example. There may bemany variations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A semiconductor device, comprising: a gatedisposed over a substrate; a source region and a drain region onopposing sides of the gate; and a pair of trench contact openings overand abutting an interfacial layer of at least one of the source regionand the drain region, the interfacial layer comprising boron; and aconformal layer comprising boron disposed within the pair of trenchcontact openings.
 2. The semiconductor device of claim 1, wherein theconformal layer comprises amorphous boron.
 3. The semiconductor deviceof claim 1, wherein the conformal layer comprises substantially pureboron.
 4. The semiconductor device of claim 1, wherein the conformallayer comprises 100 atomic % boron.
 5. The semiconductor device of claim1, wherein the conformal layer comprises at least 98 atomic % boron. 6.The semiconductor device of claim 1, wherein the interfacial layer has athickness in a range from about 0.5 to about 2 nanometers (nm).
 7. Thesemiconductor device of claim 1, wherein the pair of trench contactshave sidewalls that contact the interfacial layer.
 8. The semiconductordevice of claim 1, wherein the semiconductor device is a p-type fieldeffect transistor (PFET).
 9. The semiconductor device of claim 1,wherein the trench contact comprises a high-k dielectric material. 10.The semiconductor device of claim 9, wherein the high-k dielectricmaterial contacts the interfacial layer.
 11. The semiconductor device ofclaim 9, wherein the trench contact further comprises a conductivemetal.
 12. The semiconductor device of claim 11, wherein the conductivemetal is tungsten, aluminum, platinum, gold, or any combination thereof.13. The semiconductor device of claim 9, wherein the high-k dielectricmaterial is HfO₂, ZrO₂, Al₂O₃, TiO₂, La₂O₃, SrTiO₃, LaAlO₃, Y₂O₃, apervoskite oxide, or any combination thereof.
 14. The semiconductordevice of claim 1, wherein the pair of trench contacts have a base thatcontacts the interfacial layer.
 15. The semiconductor device of claim 1,wherein the interfacial layer comprises at least 99 atomic % boron. 16.The semiconductor device of claim 1, wherein the interfacial layercomprises boron in an amount in a range from about 1×10²² to about3×10²² atoms/cm².
 17. The semiconductor device of claim 1, wherein theinterfacial layer comprises 100 atomic % boron.
 18. The semiconductordevice of claim 1, wherein the interfacial layer comprises at least 98atomic % boron.
 19. The semiconductor device of claim 1, wherein thesubstrate comprises silicon.
 20. The semiconductor device of claim 1,wherein the substrate comprises silicon germanium.